this is my ugly solution for now!
Dim aw As UInteger = com.tilesizewidth + pnt.X
Dim ah As UInteger = com.tilesizeheight + pnt.Y
If multisel Then
aw = pnt2.X
ah = pnt2.Y
multisel = False
drawselrect = False
selectedfirstpnt = True
End If
Dim edit = New Bitmap(sourceimg)
For i As Integer = pnt.X To aw
For j As Integer = pnt.Y To ah
edit.SetPixel(i, j, Color.Transparent)
Next
Next
sourceimg = edit